I heard EA was banning people who bought legit BF3 but used the 'crack' that razor1911 made for legit buyers to avoid origin.
If you have nothing to hide, get origin. But I have heard it scans your entire PC for EA content so they would probably detect pirated software.(if you pirated any of their other games, but bought BF3 legitimaately)
Whether they'd do anything about it is the question...